Researchers at Texas A&M University have successfully "knocked down" the expression of possible disease-causing genes in a cloned goat fetus, perhaps paving the way for breeding disease resistance in other animals, even those genes that might cause bovine spongiform encephalopathy (BSE), commonly known as Mad Cow Disease.

Researchers Mark Westhusin and Charles Long in Texas A&M's College of Veterinary Medicine & Biomedical Sciences, working with fellow scientists Greg Hannon, Michael Golding and Michelle Carmell at the Howard Hughes Medical Institute's Cold Spring Harbor Laboratory, successfully utilized genetic engineering to produce a goat cell line in which the gene encoding for prion protein (PrP) was targeted for silencing by a process known as RNA interference. They then utilized these cells for nuclear transfer to produce a cloned, transgenic goat fetus which exhibited a greater than 90 percent knock down of PrP. Previous studies involving mice in which the PrP gene has been silenced have demonstrated the animals to be resistant to prion-mediated diseases such as BSE.

Their work is published in the current Proceedings of the National Academy of Sciences.

Their success raises the possibility of introducing the same technology into cattle to prevent numerous diseases. "The exciting part is that we may be able to use this technology to prevent other diseases from ever starting," Westhusin explains.

"We were able to knock down the genes that are involved with diseases in goats. In cattle, the disease that would most likely be targeted would be BSE, although there are numerous other genes that could be targeted to produce animals resistant to a variety of diseases. Moreover, the success raises possibilities to develop similar disease resistance strategies in other animal species," Westhusin adds.

BSE, or Mad Cow Disease, is a fatal brain-wasting disease first identified in the United Kingdom in 1986. BSE affects a cow's nervous system and causes the animal to lose much of its movement before it eventually dies.

More than 180,000 cases of BSE have been confirmed worldwide, including recent cases in the United States. The disease can be passed to humans, and more than 100 such cases have been confirmed, most of those in England.

"The next step is to try and avoid the cloning process - to skip that step if possible in developing the disease resistant animals," Westhusin says. "That's where more research is going to be needed and where the process goes from here."

Westhusin has been involved in several cloning "firsts," among them the first cloning of a cat in 2002 and a white tailed deer in 2004.